Tama Soil Series

Tama is a very deep, well drained prairie soil found on gentle upland slopes and stream terraces in eastern and central Iowa.

What makes Tama easy to recognize is its thick dark topsoil. That surface formed under tallgrass prairie, while the whole profile developed in loess, the fine windblown silt that blankets much of eastern Iowa.

Below the dark surface, Tama has a clay-enriched subsoil that holds water and plant nutrients. That mix of deep rooting space, good drainage, and silt-rich parent material makes it one of Iowa's classic crop soils.

The Tama series was established in Black Hawk County, Iowa, in 1917. It was named for Tama County, following the USDA practice of naming soil series after a nearby place.

Soil scientists use Tama as Iowa's representative state soil because it matches the state's best-known upland prairie farmland. It is deep, well drained, dark, and widespread across the loess-covered farm belt.

Educational soil programs identify Tama as Iowa's state soil, but StateSymbolsUSA lists it as a representative soil rather than a legislatively adopted state symbol. That is why Tama is widely recognized even though Iowa does not appear to have a formal state-soil law.

If you dug into Tama soil, the first thing you would notice would be how dark the topsoil is. That dark layer is thick because prairie roots added organic matter year after year before the land was farmed.

Below the topsoil, the profile turns browner and more clay-rich. Deeper still, it fades into lighter loess, the windblown silt from which the whole soil formed.

Tama soil is found mainly in eastern and central Iowa on uplands, side slopes, and stream terraces. It covers about 933,000 acres and has been mapped in 28 counties in the state.

It is most common where loess is thick and the land rolls gently enough for runoff to leave the surface without keeping the soil wet for long periods. Tama County lies near the center of this belt.

Tama also occurs in Illinois, Minnesota, and Wisconsin, but Iowa has the largest share and the best-known farm landscape built on it.

Most Tama soil is used for crops. The principal crops are corn, soybeans, small grains, and legume hays, according to the USDA series description.

Tama is productive because it is deep, well drained, and rich in organic matter. Rain can move through it, roots can push deep into it, and the silty loess holds water well enough to carry crops through dry spells.

Before farming, Tama supported tallgrass prairie with big bluestem, little bluestem, switchgrass, and other native grasses. Today only small prairie remnants remain, while most Tama ground is planted to row crops.